Elsevier

Applied Surface Science

Volume 273, 15 May 2013, Pages 502-506
Applied Surface Science

The effects of low power density CO2 laser irradiation on graphene properties

https://doi.org/10.1016/j.apsusc.2013.02.069Get rights and content

Abstract

We report the investigations on structural modifications in monolayer graphene induced by low-power-density CO2 laser irradiation (2–60 W/cm2). Observed modifications in graphene include the disassembly of crystalline graphene into nanocrystalline structure and the generation of amorphous carbon. It was found that thermal effect played an important role during laser irradiation. By adjusting laser power density, irradiation time and temperature, the structure of graphene can be modified accordingly in a controlled manner. Our approach may enable high-efficiency and economical modification of large-area graphene, which relies on large-area irradiation using low-power-density laser.

Highlights

► Graphene structure was modified in a controlled manner by CO2laser irradiation. ► Thermal effect played an important role in CO2 laser irradiation on graphene. ► CO2 laser may enable high-efficiency and economical modification of graphene.

Introduction

Graphene [1], a two-dimensional (2D) sheet of carbon atoms arranged in a honeycomb lattice, has attracted tremendous attention and research efforts in recent years due to its exceptional transport properties, chemical stability and scalability of graphene devices to nano-dimensions [2].

Recently, it has been shown that laser irradiation can modify graphene quality and properties by reducing graphene layers [3], cleaning surface [4] and patterning [5]. However, all these reported works involve the use of either high power density lasers or expensive femtosecond laser [6], [7]. For example, Roberts et al. [7] showed that the femtosecond laser provided a relatively high accuracy in controlling the number of layers of the thinned graphene. A single-shot damage threshold in their study was identified to be as high as 3 × 1012 W/cm2. Krauss et al. [4] reported the investigations of structural modifications in single-crystal graphene due to laser irradiation at power density of 8 × 105 W/cm2. The modifications made to graphene included the removal of dopants and the gradual local decomposition of single-crystal graphene into a network of interconnected nanocrystallites. Comparing to these graphene irradiation applications using high-power-density lasers, CO2 laser can be an economical alternative for industry applications due to its wide use and low cost. However, the effects of low–power-density CO2 laser irradiation on graphene have not been investigated. In addition to the practical significance, the influence of the long-wavelength-laser irradiation on graphene properties is of fundamental science interest.

In this paper we report the investigation into the effects of CO2 laser irradiation on graphene. Specifically, we examine the interaction between long-wavelength-laser and graphene at different power densities. We attempt to show the feasibility of controlled graphene structure modification using laser with low power density.

Section snippets

Experimental setup

Samples of monolayer graphene sheets were prepared by chemical vapor deposition (CVD) on a Si substrate coated with 300 nm thick oxide. Each sample was irradiated by a CW CO2 laser for 5 min at one of the five different power densities: 2 W/cm2, 13 W/cm2, 30 W/cm2, 43 W/cm2 and 60 W/cm2, respectively. The diameter of the laser beam was 4 mm so that the whole sample could be irradiated. Irradiation was carried out under vacuum conditions (10−3 Pa) in order to avoid interactions with atmosphere. The

Results and discussion

Fig. 3a shows the Raman spectra of the pristine graphene and the graphene samples under laser irradiation of different power densities. These spectra manifest three important features: the disorder D peak, the zone-center G peak and the second-order 2D peak near 1350, 1580 and 2680 cm−1, respectively. For the pristine graphene, the disorder D peak is not obvious, which indicates its highly ordered crystalline structure [8].

Fig. 3b depicts the change in both the D peak and the 2D peak relative to

Conclusion

In summary, we have demonstrated that graphene structure can be modified by CO2 laser irradiation at low power density. Graphene experienced two processes under laser irradiation: (1) when the power density was low, crystalline graphene disassembled into nanocrystalline structure, which caused a dramatically increase of ID/IG. (2) when the power density increased past a certain threshold, hydrogenated amorphous carbon formed on the surface, which caused a slight decrease of the ID/IG and the

Acknowledgments

The authors greatly thank the funding support by China National Key Basic Research and Development Program (2011CB013000), British Royal Academy of Engineering and Tsinghua University Initiative Scientific Research Program (2010THZ0).

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